Friction material



Patented Nov. 2, 1937 2 98 978 UNITED STATES PATENT OFFICE FRICTION MATERIAL William L. White, Clifton, N. J., assignor to Raybestos-Manhattan, Inc., Passaic, N. J., a corporation of New Jersey No Drawing. Application October 7, 1933, Serial No. 692,619

4 Claims. (01. 1067.5)

Friction materials such as brake linings, brake In my process, I take rubber that has been preblocks, clutch facings, and the like have been viously vulcanized and grind and pulverize it made of woven asbestos fabrics or tapes impreguntil it can be passed thr u a 20 esh W nated or bonded together with such materials screen. Then, in any suitable mixer, such as as oxidized oils, natural and artificial asphalts, a tumbling barrel or a Werner-Pflei-derer mixer, 5 synthetic resins and rubber. Likewise, many I mix intimately about parts of this finely types of friction materials have been produced powdered rubber dust with 60 parts of asbestos by saturating asbestos millboard or felted asfiber and 30 parts of some suitable resin such as bestos fibers with similar types of binders, or phenol resin, mold this mixture under sufiicient l0 asbestos fibers have been mixed with rubber or temperature and pressure to make the resins in- 10 like binders and then molded under pressure and. f sib e, and p oduce a ha dense a of t heat to hard segments of desired size and shape. pr per size and sh p he rf e r l y In all of the above cases the use of the saturant round, and the friction material is then ready or binder has been primarily to give the resultant for use.

products strength and rigidity. In the resultant block or facing there are dis- 15 I have found that the successful operation of tributed uniformly throu hout its ma s t great friction materials such as brake linings or brake number of minute rubber particles, each of which blocks demands that there be a very slight lubriwill act separately to properly lubricate at high cation. When the brakes are engaged in a movtemperatures the areas immediately adjacent to 2d ing Vehicle, very high almost instantaneous sur- 'it. The prime function of the rubber is to proface temperatures are developed. These tempervide these dots of lubrication. The prime funcatures may often exceed 1,000 F. Where dry, tion of the resin is to serve as an infusible binder harsh friction materials are used, if there is no to hold the mass together. Since the high temlubrication present, then under high temperape 'at e s p m y a flesh Surface temperetures and pressures the brake drums are readture, then only the dots of rubber exposed to the 25 ily scored or the braking application is acsurface will act as lubricating spots, and the parcompanied by excessive noise, squealing and ticles of rubber underneath the surface remain chatter. However, if a very limited and proper p ac a y un an e AS the lining Wears dOWh, amount of lubrication be present; then the these new dots of rubber are exposed, th vbraking operation can be made smoothly, quieting a constant lubricating surface throughout the 30 ly, and with greatly reduced tendency toward life of the lining or facing. Obviously, I can sescoring of the drums. The need for this cure any degree of high temperature lubrication lubrication is greatest when the temperatures y e D D of rubber used and, t0 some and pressures are the highest. When temperaglee, y the Particle Sizetures and pressures are low, the lubrication of While I p e o use rubber as the lubricant, 35 these friction materials is quite likely to intery t I (10 not co fi myself solely to rubber- I fere with the proper braking action, so the probcan use crystalline or granular materials, such lem resolves itself into the use of a material as the chlorinated diphenyls (aroclors), the very which will lubricate to a limited degree at high high melting point natural esphaltums, Such as temperatures but will have little or no lubricat- G a e d W t t e h ti 40 ing properties at low temperatures. point hydrocarbons that result from the distilla- I have found that soft, vulcanized rubber post on f a p 00811 and the like, sesses these qualities to a marked degree; t such plasticizers as paratoluenesulfonanilid or high temperatures it has. sufficient lubricating hlori ate naphth l n n securing y qualities if used in a limited quantity, and at low an zed ru ber, I an use vul an ed vir in rub- 45 temperatures instead of being a lubricant it is er with 2 to 6% of sulphu nd then pulVeriZe quite high in coefiicient of friction. I am aware d c e I m y use y Suitable Scrap that rubber has been used in friction materials, sed vul ani ed r bb r- I pr r to use n y soft but it has always been used as a binder. True, rubber with sulphur not exceeding 6%, but I can additional binders, such as phenol resins, have u W h pe ps lesser efiectiveness, Powdered 50 been used with the rubber binder, but in all hard rubber dust, but in no case do I depend cases sufiioient sulphur has been added to the pon he rub r a a in its p m f n i n is composition to vulcanize the rubber to hard ruba hi te perature lubricant that will have little her because rubber acts as a useful binder in fric- 1' 0 lubricating effects at low temperaturestion materials only if it is vulcanized hard. As binders, I prefer to use a dry, powdered, 55

binding resin, but obviously I can secure binding properties with liquid as well as with powdered resins. Any type of conventional binder may be used includmg oxidizable oils, natural and artificial asphalts, and I can use any type of polymerized binder or any condensation product which will not soften to too great a degree under heat to properly function as a binder; I can use any type or length of asbestos fiber needed. These fibers can be mixed in any convenient way with the rubber particles and binders and can either be a loose mix which will be compressed or can be felted or made into asbestos millboard, or can be spun into yarns and woven or braided into fabrics. If felted or made into millboard the asbestos and the non-metallic lubricating materials can be mixed in the beater. and the binder added as a separate operation or all three ingredients can be mixed at one time in one operation. In applying the invention to the manufacture of friction materials fromwoven or braided fabrics the rubber dust and binder in powdery condition may be dusted into the asbestos on the carder. In addition to these three basic elements, I can add any other desirable pigments or fillers.

It is to be understood, of course, that the specific proportions named in the illustrative example may be varied widely, depending on the type of binder used and the frictional use or abuse to which the particular friction material being made is to be put.

By high temperatures I refer to the temperatures secured by repeated stopping of an automobile traveling at the speed of 40 miles per hour with a deceleration rate of not less than feet per second per second, two such stops per mile. By relatively low temperatures I refer to the temperatures secured by the stopping of an automobile traveling at the speed of miles per hour with a deceleration rate of approximately 5 feet per second per second, repeating such stops not more than one per mile.

I claim as my inventiorif 1. Friction material, comprising a hard, dense mass of asbestos fibers and an organic binder cured to provide the desired coefiicient of friction, having distributed therethrough a relatively small amount of finely divided particles of vulcanized soft rubb er having the property of melting to lubricate the working surface of said friction material at relatively high temperatures and of such a character that they will not melt to lubricate the working surface of said friction material at relatively low temperatures.

2. Friction material, comprising a hard, dense mass of asbestos fibers and a binder cured to provide the desired coeflioient of friction, having distributed therethrough a relatively small amount of finely divided soft rubber particles comprising sulphur in a quantity not exceeding 6% and which particles will melt to lubricate the working surface of said friction material at relatively high temperatures but which will not melt to lubricate said surface at relatively low temperatures.

3. Friction material, comprising a hard, dense mass of asbestos fibers and a binder cured to provide the desired coeificient of friction, having distributed therethrough a relatively small amount of finely divided soft rubber particles comprising'sulphur in a quantity not exceeding 6% and which particles will melt to lubricate the working surface of said friction material at relatively high temperatures but which will not melt to lubricate said surface at relatively low temperatures, characterized in that the rubber particles are present in an. amount, by weight, less than the binder or the asbestos.

4. A friction material composed of 60 parts of asbestos fibres, parts binder and 10 parts of finely divided soft rubber particles uniformly distributed throughout the mass.

WILLIAM L. WHI'I'E. 

